Most of the currently available carbon rods for arc gouging process use electroplated copper as their primary conducting material. As can be seen in FIG. 1, in a conventional way of forming a gouging carbon rod, every carbon rod 10 is coated with an electroplated copper layer 12 by electroplating copper plates 11 to the carbon rod 10, so that the produced carbon rod or electrode has reduced electrical resistance to conduct a high current needed to generate arc. However, smoke hazardous to human body will be produced in the process of burning copper at high temperature.
Further, the existing electroplating copper process also produces a large quantity of copper ion-containing waste water and acidic gas, which tend to cause heavy metal pollution in water, soil and air. Therefore, pollution control facilities must be correspondingly provided in response to the increasing sense of environmental protection. Such pollution control facilities will doubtlessly increase the manufacturing cost of the gouging carbon rod.
Since the conventional way of electroplating copper to the carbon rod has the disadvantage of being hazardous to the living environment and human body, aluminum is used to replace copper in producing the carbon rod. In view that the aluminum material could not be adhered to the carbon rod by way of electroplating, a so-called metal thermal spraying technique is currently used for spray coating high-temperature molten aluminum material on the surface of the carbon rod. However, with the metal thermal spraying technique, the sprayed aluminum coating has to be re-processed by re-melting it at a temperature close to the melting point of aluminum. That is, the current metal thermal spraying technique will consume tremendous power energy and is inconvenient to use.
Another type of gouging carbon rod with aluminum coating has been developed in an attempt to overcome the problem of large power energy consumption. To produce this type of gouging carbon rod, first coat an aluminum material on the surface of the carbon rod by way of the metal thermal spraying technique, and then sinter the aluminum-coated carbon rod at a temperature below the melting points of metals. A disadvantage of the conventional metal thermal spraying technique is that only a considerably small quantity of aluminum material can be adhered to the surface of the carbon rod via this technique and therefore forms waste of metal material. In addition, the aluminum material tends to oxide, resulting in poor adhesion between the coated metal layer and the carbon rod surface and higher electrical resistance of the carbon rod. Under these circumstances, the carbon rod is easily consumed to have short service life. Further, the sintering process also consumes additional power energy and is therefore not economical for use.
To overcome the difficulties in using aluminum as the conducting material of the carbon rod, there is developed an extrusion molding method, in which a conductive metal material is coated with a mixture of artificial graphite, which serves as a major material, and binders, such as coal tar and asphalt, before being sintered at a temperature lower than melting points of metals in an inactive environment. However, the currently available carbon rod electrode requires a sintering temperature higher than 1000° C., which is higher than the melting points of most metals. On the other hand, a carbon rod electrode sintered at lower temperature would have higher electrical resistance. And, the sintering process conducted in an inactive environment filled with an inert gas requires high cost and does not support continuous production.
There is also developed a gouging carbon rod formed by inserting a metal rod into a carbon rod and then sintering the assembly at a temperature lower than melting points of metals. Due to the sintering temperature lower than metal melting points, the produced gouging carbon rod has the problem of insufficient adhesion between the metal and the carbon rod.
In view of the above drawbacks and disadvantages in the existing carbon rods, it is necessary to develop new manufacturing method and structure for the carbon rod, particularly the gouging carbon rod.